There have already been described electric conductors for withstanding high temperatures, said conductors being constituted by wires of metal (generally copper), which is a good conductor, coated with nickel or gold, for example, to which an enamel made of a heat resistant synthetic resin is applied. When the conductor is made of copper not coated with another metal, since insulating enamels are often partially porous to air, an oxide layer forms as soon as the temperature rises above 250.degree. C. Said oxide layer considerably reduces the adherence of the enamel on the conductor. This is detrimental to the thermal conduction phenomenon and to the mechanical strength of the insulation assembly. There is also an interface between the copper and the protective metal where phenomena of diffusion of one metal into the other occur. This reduces the effectiveness of the protection. Lastly, in the case of conductors intended for high-frequency current, since the superficial electric conductivity of the protective metal is higher than that of copper, the current is even more concentrated at the surface of the conductor and causes extra heating of the enamel.